<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <p id="app">10:10:01</p>
    <script>
        function handleTime(value){
            if(value<10){
                return "0"+value;
            }
            return ""+value;
        }
        function showTime(){
            var app = document.getElementById("app")
            var endTime = "2020-12-04 16:50:00";

            endTime = new Date(endTime).getTime();

            var nowTime = new Date
        }
    </script>
</body>
</html>